Reliability and safety of tension leg platforms

This paper is concerned with structural safety of tension leg platforms (TLPs) in extreme storm waves. Based upon selected statistical models for the distributions of water surface elevation during a storm, mean storm wind velocity, structural strength and storm arrivals, a reliability model for the mooring system of the TLP is presented. It is used to assess the probability of progressive failure of the legs at each corner and the reliability of the mooring system during the service life of the platform as a function of various design parameters.     

Surrogate‐based toll optimization in a large‐scale heterogeneously congested network

Toll optimization in a large‐scale dynamic traffic network is typically characterized by an expensive‐to‐evaluate objective function. In this paper, we propose two toll‐level problems (TLPs) integrated with a large‐scale simulation‐based dynamic traffic assignment model of Melbourne, Australia. The first TLP aims to control the pricing zone (PZ) through a time‐varying joint distance and delay toll such that the network fundamental diagram (NFD) of the PZ does not enter the congested regime. The second TLP is built upon the first TLP by further considering the minimization of the heterogeneity of congestion distribution in the PZ. To solve the two TLPs, a computationally efficient surrogate‐based optimization method, that is, regressing kriging with expected improvement sampling, is applied to approximate the simulation input–output mapping, which can balance well between local exploitation and global exploration. Results show that the two optimal TLP solutions reduce the average travel time in the PZ (entire network) by 29.5% (1.4%) and 21.6% (2.5%), respectively. Reducing the heterogeneity of congestion distribution achieves higher network flows in the PZ and a lower average travel time or a larger total travel time saving in the entire network.     

Coupled dynamics of tensioned buoyant platforms and mooring tethers

A mathematical model is presented of the coupled dynamics of a tensioned buoyant surface platform and the lateral dynamics of its taut mooring tethers. A finite element model of the lateral mooring tether dynamics is extended to take account of nonlinear square law fluid damping by a simple global ‘whole tether’ linearization and an alternative computationally more expensive ‘element-by-element’ linearization scheme. The resultant finite element model is combined with the surface platform dynamic analysis and the coupled dynamic model is used to investigate the effects of water depth, surface platform mass and tether mass per unit length on the tether displacements and bending stresses as well as the resultant surface platform displacements. The results show that the bending stresses induced in the tethers due to their dynamic motions are quite small and that the tether dynamics only affect the motion response of the platform appreciably if the tethers are long (1500 m or more), have a large mass per unit length and have a relatively low tension; or if the platform mass is relatively small. It was also found that the additional computing time required for the local ‘element-by-element’ equivalent linearization was not matched by the small improvement in accuracy obtained over the global ‘whole tether’ technique.     

肋环型索穹顶初始预应力分布的快速计算法

肋环型索穹顶是美国工程师Geigcr根据Fuller的张拉整体结构思想开发的一种新型预张力结构，并最早应用在汉城奥运会的体操馆和击剑馆。考虑到该结构是一种轴对称结构，本文提出了确定初始预应力分布的快速计算法．该法从平面径向桁架节点平衡关系入手，推导了不设和设有内拉环的肋环型索穹顶预应力杆内力一般性的计算公式。对特定参数的索穹顶结构还给出了内力计算用表。通过本文提供的分析方法、计算公式和内力计算用表，可方便快速地确定肋环型索穹顶结构的初始预应力分布，为该类结构的进一步设计和力学性能分析提供基础。     

Heaving response of a large floating platform

In this paper, we tackle a new dynamic problem of a large floating platform in a heaving harmonic motion due to 9000 performers or people simultaneously jumping in mass events. The objective is to estimate the heaving response of the floating structure so as to establish whether the participants will be at ease during their performances. By assuming the platform as a rigid body, the added mass and the radiation damping coefficient are first estimated. This requires the evaluation of a three-dimensional velocity potential governed by Laplace’s equation. The Green's function method was used to solve the boundary value problem. Based on the estimated added mass and radiation damping, we employ the finite element software NASTRAN to solve the transient dynamic problem for the displacement and acceleration responses. The impulse force used for the transient problem is based on experimentally obtained ground reaction force (due to a human jumping) as measured by using a force plate. As the floating platform may be dismantled and reconfigured into other shapes, two different sizes of floating platform as well as different number of jumps were considered in this study.     

最小地震剪力系数对隔震结构抗震性能的影响

最小地震剪力系数是隔震结构设计的关键控制因素之一。对等效周期为2~6s的单质点隔震体系在远场地震动（FF地震动）、近场含脉冲地震动（NFWP地震动）和近场不含脉冲地震动（NFWNP地震动）作用下的剪力系数分布特点进行分析,并将其与规程中有关最小地震剪力系数的相关规定进行对比,探寻在不同抗震设防烈度下,不能满足最小地震剪力系数的隔震结构的等效周期范围。以位于我国抗震设防烈度8度区的某隔震结构为例,采用三种不同的设计地震剪力取值方法,设计了6种不同的结构模型。通过模型的弹塑性时程分析,比较了地震动的近远场特性对各模型抗震性能的影响,及其在罕遇地震作用下的性能差异。分析结果表明：地震动的近远场特性对隔震结构的楼层设计剪力影响较大;对不满足最小地震剪力系数要求的隔震结构,采用放大设计地震剪力使其承载力满足最小地震剪力系数的方法,能够有效提高其抗震能力;不考虑最小地震剪力系数对结构设计地震剪力的限制,采用结构的实际地震剪力需求进行设计的隔震结构能够满足地震作用下的承载力和层间位移限值要求。     

非平整场地上输电塔-线体系在多点激励下的地震反应

在以往的大地震中输电塔的破坏时有发生,输电塔倒塌的部分原因是由于相邻塔在地震动多点激励下异相振动产生的导线拉力引起。本文考虑导线的几何非线性,建立了输电塔-线体系三维有限元模型,分析了非平整场地上的结构体系在地震动纵向多点激励下的反应。基于经验相干函数和修正金井清功率谱密度函数模型模拟了空间变化地震动,分别考察了地震波视波速和相干损失对于结构体系地震反应的影响。结果表明,假定地震动一致激励不能准确评估结构体系的反应,地震动空间变化效应放大了输电塔和导线的地震反应,在强震作用下,忽略地震动的空间变化会严重低估输电塔-线体系的反应。     

Wind loading effects on a catenary

The effects of wind loads on the static profile and force transmission efficiency of a tether tied to a kite-like aerodynamic body has been theoretically examined. Two important parameters which characterize the behavior of the tether have been obtained. These are the tether weight parameter, which is the ratio of tether weight to the tether tension, and the wind load parameter, which is the ratio of wind load to the tether weight. Results obtained from five different tether models (straight line, catenary, constant velocity, variable velocity and maximum stress) have been compared to determine regions of applicability of these models in terms of the above two parameters.     

波浪和地震作用下高桩承台-土-结构动力响应

利用有限元软件ANSYS模拟高桩承台-土-上部结构在波浪和地震共同作用下的内力和变形,采用Morison方程计算波浪力,并对结构水平方向输入E1-Centro波进行模拟,根据时程曲线分别选取初始状态和正负加速度最大状态对结构进行研究,研究了桩基础在波浪和地震共同作用下的位移、弯矩、剪力以及轴力的变化,并与地震单独作用下...     

索杆张力结构自应力模态分析及预应力优化

分析了现有各种求解索杆张力结构初始预应力方法的局限性,充分考虑对称性和整体可行性,从平衡矩阵理论出发利用奇异值分解法提出了一种旨在求解各种张力结构体系的整体自应力模态的求解方法,并对具有多个整体自应力模态的索穹顶结构采用修正单纯形法、以外圈环索初内力最小为优化目标进行了预应力优化。研究表明,充分考虑对称性和整体可行性的奇异值分解法能求解各种体系的整体自应力模态,预应力优化能求得满足条件的合理初始预应力分布。     

Offshore Triceratops Under Impact Forces in Ultra Deep Arctic Waters

In the recent years, offshore oil drilling and production is moving towards ultra-deep Arctic region which demands an adaptable structural form. Apart from the environmental loads, offshore structures in Arctic region will also be subjected to impact forces arising due to ship platform collision. Such loads may endanger the safety of the platform due to the combined effect of reduced temperature and impact forces on the material and geometric properties of the structure. Thus, there is a need to understand the behaviour of offshore structures under impact forces in low-temperature conditions. Offshore Triceratops is one of the recent new-generation compliant platforms proved to be suitable for ultra-deepwater applications. The main aim of this study is to assess the response of triceratops under impact forces in Arctic environment numerically. As the buoyant legs of triceratops are susceptible to impact forces arising from ship platform collision, the numerical model of a buoyant leg is developed using Ansys explicit dynamics solver. The impact analyses is then carried out with rectangular box-shaped indenter representing the stem of a ship, under both ambient conditions and Arctic temperature (− 60 °C) and the local response of the platform is studied through force deformation curves and stress contours. In order to study the global response of the platform, the numerical model of triceratops is developed in Ansys Aqwa solver and analysed under the action of impact load time history obtained from explicit analysis of buoyant leg. The impact load on the buoyant leg resulted in the continuous periodic vibration of the platform. Furthermore, parametric studies were also carried out to investigate the effect of indenter velocity, size, and location on the impact response of triceratops under Arctic temperature, and the results are discussed.     

Stabilität eines Fachwerkkragbalkens mit seitlich festgehaltenen Zuggurtknoten und mit steifem,am Auflager eingespanntem Druckgurt

Stability of trussed cantilever with laterally supported tension‐chord's nodes and a stiff compression‐chord clamped at the cantilever's supported end. For trussed cantilever with the laterally supported tension‐chord's nodes and a stiff compression‐chord which is laterally clamped at the cantilever's supported end simple formulas are derived for the beam's critical load and the corresponding compression‐chord's maximal longitudinal force. Three load cases will be discussed, namely a system of nodal forces equivalent to a uniform load, a concentrated load at the free end of beam and the combination of these two load cases. The investigation is performed firstly on the basis of the discrete structure system applying the approximate method of splitting the load into partial loads and then on the basis of the equivalent continuous model with “smeared” geometrical stiffness‐ and load data. The paper intends to contribute to an easy design and an economic analysis of the structure. Besides, it shows that even in time of involved computer analyses simple approximate methods yield valuable services.     

深海风电张力腿平台研究进展

深海区域具有发展风电的独特优势。对支撑风力机的张力腿平台的概念及形式进行简单回顾,并对该平台进展和特性研究。可知张力腿平台因稳定性好、风浪作用下动态响应小和造价相对较低而具有较强的发展潜力,对深海风电的发展具有重要的意义。     

CCTV新台址主楼外筒关键节点设计与构造

CCTV新台址主楼采用支撑筒体结构体系,外筒蝶形节点以及柱脚节点是其中的关键性节点。本文通过对蝶型节点的有限元分析,提出此类节点简化的设计方法,保证了在支撑构件屈服时,蝶型节点能基本保持弹性,满足"强节点、弱杆件"的结构抗震要求。通过与节点模型试验结果的比较,验证了这一设计方法的正确性。由于塔楼双向倾斜,且在结构高位有连体结构,造成部分外筒SRC柱柱脚在竖向荷载作用下出现拉力,与水平荷载作用下拉力叠加后进一步增大。由于水平荷载作用方向的不确定性,柱脚也可能承受较大的压力。根据柱脚受拉程度的不同,结构设计中分别采用了露出外包式、埋入式两种不同的柱脚构造形式,并在外包式柱脚中采用了高强预应力锚栓来平衡柱脚的拉力。     

A comparative study for the performance of encased granular columns

This paper describes a three-dimensional (3D) numerical analysis of a test embankment on geotextile-encased columns (GECs), in comparison with two-dimensional (2D) axisymmetric and plane strain analyses. The 3D numerical analysis was performed considering a rectangular strip under the embankment centerline. The 2D analysis was also carried out using axisymmetric unit cell and plane strain approaches. Numerical results indicated that the adopted 3D strip model represented well the measured deformations and pore pressure evolution during embankment construction and post-contraction periods. Unlike the unit cell model, both plane strain and 3D analyses could properly determine the settlement profile along the embankment base as well as the profile of the horizontal soil deformation beneath the embankment toes. The plane strain analysis, however, was not able to compute the geotextile ring force which might be simply calculated using the axisymmetric unit cell approach. The paper also showed that, due to horizontal boundary fixities applied to the embankment borders, the unit cell model clearly underestimated the tension developed in the basal geogrid.     

车辐式张拉结构张拉过程模拟分析及张拉方案研究

车辐式张拉结构造型轻盈通透,常作为大跨度体育场建筑的屋盖结构形式.对于由索杆组成的车辐式张拉屋盖结构而言,屋盖施工常常采用整体张拉成型的方法,其张拉方案的制定以及张拉过程中"力"与"形"的控制是施工张拉过程的核心内容.分析制定张拉方案所应当遵循的原则,并以深圳宝安体育场屋盖结构为例,对拟制定的3种张拉方案进行张拉过程数值模拟分析,同时依据数值分析结果评估各种张拉方案的优缺点.     

天文台圈梁移动台车设计及应用

本文介绍了在贵州天文台射电望远镜FAST主动反射面主体支承结构索网架设工程中,一种能在圆形轨道上移动的特种锚固装置圈梁移动台车的设计及应用。该移动台车是索网架设工程在圈梁上的锚固装置,它用来锚固施工索道(挂索索道和吊篮索道)以及牵引径向索的钢绞线张拉端反力架,而它们的另一端则锚固在圈梁中心的塔架和猫道V型平台上。该移动台车用固定装置有效的固定在圈梁上,台车采用平面桁架结构体积小重量轻便于在圈梁上移动,也有利于把自身承受的索力有效的转移到了圈梁上,而极大改善了自身的受力状况,台车配有斜坡轨道可让运索车从其上经过,保证了交叉立体作业的安全。     

Spherical membranes subjected to concentrated loads

Using linear membrane theory, the contours and size of reinforcements required for spherical inflatable membranes to carry tangential, normal and oblique concentrated forces, by means of a tension field and without wrinkling, is considered. Load limits for such wrinkle-free behaviour of this class of structure are established. In the second part of the paper, nonlinear membrane equations, written with respect to the deformed configuration, are used to establish the wrinkled deformation field of spherical inflatables subjected to axisymmetric normal concentrated forces without the use of reinforcements. The ponding problem for such membranes, a possible mode of failure when concentrated forces are applied in the presence of an accumulating ponding medium, is defined and the conditions for a safe ponding process specified in terms of membrane geometry, internal inflation pressure and density of the ponding medium.     

有关单桩与群桩波浪力的探讨

以小尺度桩柱为例,以Morison方程为基础,对直立、倾斜桩柱的波浪力进行了探讨,并且通过群桩影响系数对群桩波浪力的计算进行了讨论,为波浪力的确定提供了理论依据。     

中国航海博物馆双曲面索网缩尺模型试验研究

基于中国航海博物馆的双曲面索网结构,根据几何相似原则,确定索网缩尺模型,采用EM索张力测量仪对索网的索力和位移进行测量.试验过程中,采用了横索定长、竖索张拉和竖索定长、横索张拉两种张拉方案.在两种索网张拉方案下,比较分析了试验数据与数值分析结果,并对试验过程中索节点的异常现象进行研究.结果表明,在实际施工中应采用横索定长、张拉竖索至设计内力后,再微调横索的施工张拉方案.同时,应采用可以自由偏转的索夹,以尽量减少索网格的夹角畸变.